1. Field of the Invention
The present invention relates to a method of reproducing high-speed audio data by a CD-ROM player which is capable of reproducing both audio and digital data.
2. Description of the Prior Art
Hitherto, there has been proposed a CD-ROM and a CD-I (CD-Interactive) as an optical disk capable of recording both digital data such as the data operable in computers, and video data as well as audio data such as music, voice sound and so on. The CD-ROM is a disk standardized for recording above explained digital data as well as audio data in the audio signal area, yet having compatibility with a CD (compact disk) which basically deals with acoustic signals only, whereas the CD-I is an interactive disk defined in the Mode-2 of the above-mentioned CD-ROM, and is a standardized system in which the above-disclosed computer data, video data, audio data and so on are recorded per blocks by a time division multiplex mode.
FIG. 4 is a signal processing circuit in a conventional CD-ROM player. In the figure, reference numeral 1 denotes an audio signal processing section, 2 denotes a memory for storing audio signals, 3 an audio interface, 4 a digital to analog converter (hereinafter referred to just as "D/A converter"), 5 a low pass filter, 6 a CD-ROM data processing section, 7 a CD-ROM data storage which is also used as an interface buffer memory, and reference numeral 8 denotes a host computer interface such as a small computer system interface (hereinafter referred to simply as "SCSI").
In reference to FIG. 4 the signal which had previously been modulated by the EFM (Eight-to-Fourteen Modulation) method and read in from a disk is first demodulated at an EFM demodulation circuit (not shown), and then sent to the signal processing circuit shown in FIG. 4. The input EFM demodulated data is first stored in the memory 2, and then an error check to the audio signal is performed by a CIRC (Cross Interleave Reed-Solomon Code) error checking method to correct defected audio signal if any in the audio signal processing section 1. Thereafter, if the signal read in from the disk is an audio signal, the data corrected by the CIRC error checking method is fed to the D/A converter 4 by way of the audio interface 3, and after the digital to audio conversion thereof is through, it is further fed to the low pass filter 5 where high frequency components are deleted, so that a reproduced audio signal in the form of an analog signal is finally output.
On the other hand, if the signal read in from the disk is a digital signal, the data corrected by the CIRC error checking method is fed to the CD-ROM data storage 7 by way of the CD-ROM data processing section 6, wherein an error check to the stored CD-ROM data is performed with the error correction parity codes P and Q, and after the data is corrected thereby, the digital data is fed to the interface 8, which is further sent to a host computer.
By the way, it has been a common procedure nowadays to read in the digital data at a twice or a four-time faster speed than the normal speed in order to meet with the recent increase in requirement for high-speed data processing. However, since it is necessary to reproduce the audio signal as a correct sound in case that digital data and audio data are taken in by turns from one disk, in a conventional CD-ROM player as the one shown in FIG. 4, the audio signal has to be read in at the same speed as the sampling frequency thereof. Due to this, it has been a problem to require a certain time to switch the rotation speed of the disk any time when the signal to be received from the disk is changed from audio to digital and vice versa, and therefore there has not been much merit in processing digital data at a high speed.
A simple solution to this problem has been to read in the audio signal at the same speed as that for reading the digital data, but has not been effective since the conventional CD-ROM player can not make a faithful reproduction of the audio signal at a high speed due to a change in the reproducing speed.